This invention relates to arrangements and methods for transporting narrow band, e.g. voice traffic over a broad band packet network.
Much interest has been shown recently in migrating the voice networks of enterprises and carriers from connection oriented TDM networks which have traditionally been used to carry voice traffic to broad band packet networks currently used to transport data traffic. The rationale for this is based on the current rapid rate of growth of data within most networks, to the point that data has overtaken voice in capacity carried. Thus there is now a desire to reduce costs by consolidating voice networks and data overlays to a more homogenous network where voice may be carried effectively as another type of data. This, coupled with the increasing maturity and capacity of the necessary data components (e.g. routers, ATM switches), means that Voice-over-IP and the Voice-over-ATM architectures are being studied by many industry fora. The two main protagonist technologies for the future universal data network are IP (Internet protocol) and ATM (asynchronous transfer mode), each with their own advantages and disadvantages.
At the same time, there is a desire that, in these new architectures, the two main roles of the traditional voice switch, i.e. control and media switching, are separated. This is desirable for many reasons, e.g.
to force open architectures and open protocols on the industry so as to drive up competition and to drive down prices,
to allow the control platform to ride the power curve for computing performance,
to allow an open platform for software vendors to be able to offer new services.
A typical voice-over-packet network may consist of a number of media gateways (MG) at the periphery of a packet network (IP or ATM). The function of each gateway is to provide an interface between the packet medium and another medium, e.g. analog loop, digital trunk, or another packet medium. This inter-conversion may e.g. analog loop, digital trunk, or another packet medium. This inter-conversion may include voice code conversion, packetisation, echo cancellation, silence suppression, tone detection and tone generation. These gateways are relatively simple and are controlled each by a media gateway controller (MGC). This MGC handles narrow-band call control, signalling, call routing, billing etc, and one MGC may control a large number of such gateways. However to allow such system to be scaled, the architectures allow for many such media gateway controllers within a network. These gateway controllers communicate with each other to allow a call from one MG controlled by a MGC to be terminated on another MG controlled by another MGC. Ideally the function of the mediate gateway controller should be independent of the technology of the packet fabric, but this has been found difficult to achieve.
In many recently announced VoIP (voice-over-IP) architectures, where the media gateway controller function has been separated from the media gateway function, the two gateways at either end of an IP network need to exchange their transport addresses so that they may then send voice packets to each other over an IP network. These architectures as typified by that described in the IETF drafts SGCP and MGCP, typically have the following signalling flow:
a) The originating media gateway controller sends the originating gateway a CreateConnection command with the first external endpoint (EP1) defined but no network endpoint.
b) The originating gateway selects a UDP port which it wishes to use for this call and responds with its IP address and this UDP port.
c) The originating media gateway controller passes this information to the terminating media gateway controller (which may in fact be to itself for a local call)
d) The terminating media gateway controller sends a CreateConnection command to the terminating gateway with the second external endpoint defined (EP2) and includes the originating gateway""s IP address and UDP port.
e) The terminating gateway selects a UDP port which it wishes to use for this call, makes the local connection and responds with its IP address and UDP port.
f) This information is relayed by the terminating media gateway controller to the originating media gateway controller.
g) The originating media gateway controller sends the originating gateway a ModifyConection command which includes the terminating gateway""s IP address and UDP port.
h) The originating gateway makes the local connection and the end to end connections is complete.
A typical Voice-over-ATM network consists of a set of such gateways intermeshed by ATM virtual circuits (VCCs). These VCCs carry the voice calls across the ATM network. This is similar to a tandem TDM network using a set of intermeshing trunk groups. These VCCs could be permanent virtual circuits (PVCs). However, careful planning is required to prevent the link between any two sites saturating and causing blocking of calls. An alternative approach that has been proposed is to allow the setting up of switched virtual circuits (SVCs) on demand between any two gateways. However, there is at present no simple mechanism for allowing the narrow-band call to trigger such a SVC, for defining between which points such an SVC should be established, and for binding the narrow-band call to the SVC in question.
An object of the invention is to minimise or to overcome the above disadvantages.
A further object of the invention is to provide an improved arrangement and method for carrying voice traffic over a broadband, e.g. a packet or cell based network.
According to a first aspect of the invention, there is provided a method of setting up a voice connection in a multimedia session between first and second gateways over a broadband network, the method comprising exchanging session descriptors between said gateways, and providing in said session descriptors information whereby said first and second gateways negotiate and agree on the adoption of one or more attributes for said voice connection
According to another aspect of the invention there is provided a method of transporting voice traffic over a virtual channel in a broadband network, the method comprising using a virtual channel connection indicator (VCCI) within a session descriptor to identify a virtual channel connection for that voice traffic within a bundle of virtual channel connections in an ATM trunk group on which the voice traffic is to be carried.
According to a further aspect of the invention, there is provided a method of transporting voice traffic between first and second media gateways over a virtual channel incorporated in a virtual trunk group in a broadband network, the method comprising performing a mutual exchange of session descriptors between said first and second gateways, wherein said session descriptors incorporate a virtual channel connection within the virtual trunk group for that voice traffic.
According to another aspect of the invention there is provided a method of transporting voice traffic between first and second end points over a virtual channel connection within an ATM trunk group via first and second media gateways each controlled by a respective first and second media gateway controller in a broadband network, the method comprising the steps of:
at the first gateway partially defining a session descriptor and sending the partly defined session descriptor via the first and second gateway controllers to the second gateway;
at the second gateway, receiving said partly defined session descriptor, determining a virtual channel connection, and sending to the first gateway via the second and first gateway controllers a fully defined session descriptor incorporating a virtual channel connection indicator for that virtual channel connection; and
at the first gateway, receiving said fully defined session descriptor, and in response thereto establishing a connection to the second gateway on the selected virtual channel.
According to a further aspect of the invention, there is provided method of transporting voice traffic between first and second end points over a virtual channel connection within an ATM trunk group via first and second media gateways each controlled by a respective first and second media gateway controller in a broadband network, the method comprising:
at the first gateway controller, sending a create connection command to the first gateway;
at the first gateway, acknowledging the create connection command by sending to the second gateway controller a partly defined SDP session descriptor;
at the second gateway controller, sending a create connection command together with the partly defined session descriptor to the second gateway;
at the second gateway, determining a virtual channel connection, connecting the second end point to the virtual channel connection, and sending a fully defined session descriptor incorporating the identity of the virtual channel connection via the second gateway controller to the first gateway controller; and
at the first gateway controller, sending the fully defined session descriptor incorporating the identity of the virtual channel connection to the first gateway so as to establish the virtual channel connection between the first and second gateways.
According to a further aspect of the invention, there is provided a communications data network arranged to carry both voice and data traffic, the network including means for identifying via a virtual channel connector indicator (VCCI) within a session descriptor a virtual channel connection within a bundle of virtual channel communications in an ATM trunk group on which identified virtual channel the voice traffic is to be carried.
According to a further aspect of the invention, there is provided a communications broadband network arranged to carry both voice and data traffic, the network comprising a connection fabric, a plurality of gateways each providing user access to the connection fabric and interconnected via ATM trunk groups each comprising a bundle of virtual channel connections, and gateway controllers each controlling at least one said gateway, and wherein each said gateway has means for exchanging session descriptors with another said gateway via one or more said controllers, and wherein each said session descriptor incorporates information for identifying via a virtual channel connection indicator (VCCI) within a said trunk group whereby to set up a voice connection over that identified virtual channel connection
According to a further aspect of the invention, there is provided a media gateway for use in a broadband network arranged to carry both voice and data traffic, and having means for setting up a voice connection over a virtual channel connection within a bundle of virtual channel communications in an ATM trunk group, the gateway having means for selecting or creating a said virtual channel connection, and means for signalling to a similar gateway a session descriptor incorporating the identity of that virtual channel connection.
Preferably, the voice traffic is transported on ATM adaptation layer 2 (AAL2) wherein the traffic is transported in variable length minicells in ATM cells. However, the technique is in no way limited to AAL2.
In order that both the originating and terminating gateways may connect their respective TDM endpoints to the same CID in the same VCC for the same call, communication between the two gateways via the gateway controllers is provided. Each gateway needs to know the identity of its remote peer, together with a common view of the VCCI, the CID within the VCC and, where appropriate, the voice profile.
Advantageously, the gateway identifier is formatted as an NSAP (Network Service Access Point) address. This exchange of connection information is effected via the control protocol. The mechanism comprises the exchange of addressing information via session descriptors encoded using SDP. By comparison, in VoIP, the MGC(s) transparently transport the originating gateway""s transport address and preferred encoding profiles to the terminating gateway, and then transport the terminating gateway""s transport address and preferred encoding profiles back to the originating gateway.
A VCCI is used within a SDP session descriptor to identify uniquely a particular VCC within a bundle of VCCs forming an ATM trunk group. The exchange of session descriptors enables a terminating gateway to select or create a VCC and to signal its identity to the originating gateway. Advantageously, an AAL2 channel ID within the session descriptor may be used to identify uniquely a particular CID within a VCC.
In a further embodiment, each gateway may support a set of voice profiles. A common e.g. AAL2 voice profile may then be negotiated between two gateways. This is achieved by the originating gateway suggesting a set of voice profiles in the outgoing session descriptor and the terminating gateway choosing one such profile and incorporating that information in the returned session descriptor. Similarly, a common adaptation type and/or a common connecting fabric type can be negotiated between two gateways by means of an exchange of session descriptors.
In a further embodiment, a pair of gateways may be capable of supporting a number of connection fabric types , and the session descriptors may be used to negotiate selection of a particular fabric type for the session.
The semantics of the session descriptor may be adapted for use with AAL2, as follows. The originating gateway produces a session descriptor with its ATM address specified, but with the VCCI/CID left set to any ($). Similarly this gateway sets the voice profile to a list of the profiles that it supports, consistent with the voice codec as requested by the MGC. This is delivered (via the MGCs) to the terminating gateway which then may select an available VCCI/CID to the gateway identified in the received SDP, together with a single voice profile consistent with its capabilities, the codec requested by the MGC and the list of profiles offered by the originating gateway. The terminating gateway then returns the session descriptor (via the MGCs) with its own ATM address specified, and with the VCCI/CID and profile set.
In a preferred embodiment, the invention provides a method of leveraging Gateway SDP session descriptor exchange and media gateway controllers designed for VoIP which handle these SDP session descriptor exchanges, and use them to
a) unambiguously exchange ATM VCC information such that a narrow-band call over ATM may be set-up.
b) supply relevant ATM addresses, whereby if necessary an ATM SVC connection may be established for the purpose of such a narrow-band call
c) unambiguously exchange AAL2 connection identifier information such that a narrow-band call over AAL2ATMVCCs may be set-up.
d) allow negotiation of an unambiguous AAL2 voice profile to be used by both AAL2 gateways
e) allow negotiation of the ATM adaptation layer (AAL1, 2 or 5) or the fabric itself (ATM, IP or other) to be used for this call.